Energy absorption features of 3-D braided rectangular composite under different strain rates compressive loading

There are huge potential applications of 3-D braided composite in aerospace engineering because of the non-delamination feature of the composite under impact loading. This paper presents the analysis of energy absorption features of 3-D braided composite under compression with different strain rates. The 3-D 4-step rectangular braided composite coupons were tested on a material tester MTS 810.23 and a split Hopkinson pressure bar (SHPB) apparatus to obtain out-of-plane and in-plane compression stress vs. strain curves at quasi-static and high strain rate state. The failure modes and energy absorption features of the 3-D braided composite under different strain rates were analyzed both in time domain and frequency domain. The energy absorbed by the 3-D braided composite increases with the strain rate. From fast Fourier transform (FFT) analysis of compression stress vs. time histories, the power of energy absorption of the 3-D braided composite increases with strain rate and mostly concentrate on the high frequency region. While for quasi-static compression, the power distributes in very narrow frequency region and also is less than that in high strain rates. This feature corresponds to the different damage and energy absorption mechanisms of the 3-D braided composite under quasi-static and high strain rate compression.     

Feedback median filter for robust preprocessing of glint noise

Glint noise may arise in a target tracking system. The non-Gaussian behavior of glint noise can severely degrade the tracking performance. Measurement preprocessing at the front-end of the tracker is an effective method to reduce glint noise. The preprocessor proposed by Hewer, Martin, and Zeh (1987), which used the computationally intensive M-estimator, may not be suitable for practical implementation. An alternative method employing the median filter is studied here. The median filter is well known for its simplicity and robustness. However, the efficiency of the median filter can be seriously degraded if input samples are not identically distributed. This is what we may encounter in the tracking problem. A feedback median filter is then proposed to overcome this impediment without substantially increasing complexity. Simulations show that the new preprocessor can greatly improve tracking performance in the glint noise environment.     

On Computing the Cramer-Rao Bound for a Random Signal

The Cramer-Rao bound for estimating parameters of a random signal is obtained using a sampled data approach. A numerical example is presented to illustrate the result. In two limiting cases, it is shown that this bound converges to the well-known bounds for the point and Rayleigh targets.     

基于使命任务分解的航空电子跨平台通信组织与仿真

在先进的综合化航空电子系统设计中,跨平台通信的组织将直接体现使命任务的需求。通过功能流程框图将航空电子系统使命任务各个阶段分解为功能组件,给出了一种功能组件之间跨平台信息交互的组织方法,并采用移动自组织通信的方式实现。将某任务片段中的空中图像信息传输作为模拟案例,使用OPNET软件进行仿真研究。仿真结果表明,该方法根据任务的特性设定平台之间的动态通信过程,与没有经过使命任务分解设计的对照组相比,在同等发射功率下能够有效地降低误码率。     

半球谐振陀螺控制及补偿技术

首先介绍了半球谐振陀螺(HRG)发展历程，分析国内外研究现状并总结了现阶段半球谐振陀螺发展趋势；其次讨论了半球谐振陀螺控制技术，包括不同条件下驻波的激励检测方法、陀螺工作模式、驻波控制方案，以及一种全新的频率调制控制方案；另外，分别以驻波调制补偿、电极增益补偿、多陀螺补偿以及环境载荷补偿为例，分析了控制方案补偿、器件补偿、系统补偿以及场景补偿等四种半球谐振陀螺补偿技术；最后通过对现有技术和研究的分析，提出了半球谐振陀螺控制及补偿技术未来的发展方向。     

Video watermarking synchronization based on profile statistics

A novel temporal synchronization method for video watermarking by matching the profile statistics. The profile statistics, represented by the characteristic parameters such as position mean and variance in the x-and y-directions, of a frame in a video sequence can easily be calculated and sent as side information to the receiver. At the receiving end, temporal attacks such as transposition, dropping, and insertion can be detected by comparing side information and characteristic parameters calculated from the received video. The simulation results show that the proposed method can successfully re-synchronize the attacked video back to the original format with accuracy from 72.41% to 98.15% for various video sequences based on single frame matching. After the voting process, the GOP detection accuracy can be improved to the range of from 96.30% to 100%.     

《高频电子线路》课程的手写式多媒体教学尝试

多媒体教学是现代教育技术的重要体现,但又不可完全取代粉笔 黑板的传统教学模式,论文介绍了一种将手写设备配合EduOffice电子白板软件,用于《高频电子线路》的多媒体教学的方法,可充分发挥多媒体的优势,并轻松实现粉笔 黑板的教学效果,提高了教学效率,增强教学协调性。     

基于偏置比例导引与凸优化的火箭垂直着陆制导

凸优化由于求解效率高在飞行器轨迹规划和制导中得到广泛研究应用。但是，由于火箭垂直返回制导需要考虑气动力带来的非线性，现有的凸优化求解方法或简单地采取逐次线性化近似凸化最优控制问题，经常出现收敛性问题；或需针对具体问题进行相应的系列凸化剪裁，虽然改善了收敛性，但不同模型的凸化剪裁方法差别很大，通用性较差。为此，将偏置比例导引与凸优化相结合，用以求解存在落角、落速和推力范围约束的火箭垂直返回定点软着陆制导问题。提出的制导方法将该制导问题分解为法向满足落角与落点约束的偏置比例导引，以及切向满足速度与推力约束的凸优化和滚动时域控制制导。在切向制导中，提出利用三次多项式近似飞行轨迹以方便凸优化求解，并建立剩余飞行时间的估算方法以提供给比例导引。仿真结果表明，提出的制导方法能有效满足各种约束，实现火箭精确着陆。与现有的直接采取逐次线性化近似的凸优化方法相比，提出的方法由于将制导进行切向和法向分解，大为简化了凸优化模型，显著提高了求解效率和收敛性。此外，提出的方法无需复杂繁琐的凸化处理，对于一般的推力可控且对末速存在约束的固定终端位置的制导问题皆适用。     

多雷达跟踪网数据融合算法的研究

为了将国外多传感器融合技术引用的雷达网系统中，本文对国外多传感器数据融合技术做了简要叙述，并进行了归纳，分析，作者认为在卡尔曼滤波前，对多个传感器的观测数据进行并行的预处理（融合估计）的算法比其他融合算法要求，为了找到使跟踪精度更高的数据融合算法，本文不仅就参与融合的观测值的数目与跟踪精度的关系进行了仿真比较，而且对几种认为可取的国外算法进行了扩展与改进。最后，将改进后的几种融合算法就其应用于雷达     

Coherent Doppler tomography-a technique for narrow band SAR

Some concerns regarding a technique of narrowband synthetic aperture radar (N-SAR) imaging called coherent Doppler tomography (CDT), which may be a good candidate for spaceborne applications, are addressed. Using a single-frequency signal, are addressed. Using a single-frequency signal, resolution of two tenths of a wavelength can be achieved in the point spread function if the radar platform circles the ground path to be imaged. However, the high sidelobe level of -8-dB in the point spread function results in an unacceptable dynamic range. To reduce the sidelobe level, two approaches are presented: coherent processing using multiple discrete frequencies and noncoherent subaperture processing. Simulation results demonstrate that the sidelobe level is substantially reduced by both methods. However, the resolution is degraded and the computational overhead is greatly increased for noncoherent subaperture processing. Also presented is a possible satellite geometry configuration that could utilize N-SAR processing to provide high-resolution global mapping capability